1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus provided with the zoom lens, and particularly to an image pickup apparatus provided with a solid-state image sensor, such as a video camera, a digital still camera, a broadcasting camera and a monitoring camera.
2. Description of the Related Art
As an image capturing optical system used for image pickup apparatuses such as digital single-lens reflex cameras, a compact zoom lens is required which also has a high zoom ratio and a high optical performance in its entire zoom range and is capable of performing a high speed autofocus.
The digital single-lens reflex camera is desired to perform capturing of not only still images but also moving images, and it is necessary for autofocus in moving image capturing to repetitively perform focusing operations, each being performed in still image capturing.
In a focusing operation by a contrast detection method, an in-focus direction is detected by reciprocating a focus lens unit with a high speed in an optical axis direction, which is called “wobbling”. After the wobbling, a signal component in a specific frequency band is detected from an output signal of an image sensor, an optimal, position of the focus lens unit at which an in-focus state is obtained is calculated, then the focus lens unit is moved to the optimal position, and thereby focusing is completed.
In order not to cause a use to have an odd feeling during the wobbling, it is necessary to drive the focus lens unit at a high speed if the focus lens unit has a heavy weight, an actuator such as a motor to drive the focus lens unit at a high speed become large in size, and a maximum diameter of a lens barrel increases, so that a lens apparatus including them becomes large in size.
Japanese Patent Laid-Open No. 10-39215, U.S. Pat. No. 8,049,968 and U.S. Patent Application Publication No. 2012/0026602 disclose zoom lenses each performing wobbling of a compact and lightweight lens unit disposed on the image side further than an aperture stop in focusing.
The zoom lenses disclosed in Japanese Patent Laid-Open No. 10-39215 and U.S. Pat. No. 8,049,968 each include, in order from the object side to the image side, first, second, third, fourth and fifth lens units having positive, negative, positive, positive and negative refractive powers; the fifth lens unit is moved during the focusing.
The zoom lens disclosed in U.S. Patent Application Publication No. 2012/0026602 includes, in the order from the object side to the image side, first, second, third, fourth, fifth and sixth lens units having positive, negative, positive, positive, negative and positive refractive powers; part of the fifth lens unit is moved during the focusing.
In order to achieve an entirely compact zoom lens having a high, zoom ratio and being capable of performing focusing at a high speed, it is important to appropriately set its zoom type, refractive powers of respective lens units included therein and its lens configuration.